TY - JOUR
T1 - Noncanonical Binding of Calmodulin to Aquaporin-0
T2 - Implications for Channel Regulation
AU - Reichow, Steve L.
AU - Gonen, Tamir
N1 - Funding Information:
The authors would like to thank Rachel Klevit (University of Washington) for helpful discussions and providing us with the calmodulin clone. We would also like to thank Gabriele Varani (University of Washington) for helpful discussions, critically reading this manuscript, and giving us access to the 600 MHz and 750 MHz NMR. This work was supported by NIH grant R01 GM079233. The authors declare that neither has financial interests related to this work.
PY - 2008/9/10
Y1 - 2008/9/10
N2 - Aquaporins (AQPs) are a family of ubiquitous membrane channels that conduct water across cell membranes. AQPs form homotetramers containing four functional and independent water pores. Aquaporin-0 (AQP0) is expressed in the eye lens, where its water permeability is regulated by calmodulin (CaM). Here we use a combination of biochemical methods and NMR spectroscopy to probe the interaction between AQP0 and CaM. We show that CaM binds the AQP0 C-terminal domain in a calcium-dependent manner. We demonstrate that only two CaM molecules bind a single AQP0 tetramer in a noncanonical fashion, suggesting a form of cooperativity between AQP0 monomers. Based on these results, we derive a structural model of the AQP0/CaM complex, which suggests CaM may be inhibitory to channel permeability by capping the vestibules of two monomers within the AQP0 tetramer. Finally, phosphorylation within AQP0's CaM binding domain inhibits the AQP0/CaM interaction, suggesting a temporal regulatory mechanism for complex formation.
AB - Aquaporins (AQPs) are a family of ubiquitous membrane channels that conduct water across cell membranes. AQPs form homotetramers containing four functional and independent water pores. Aquaporin-0 (AQP0) is expressed in the eye lens, where its water permeability is regulated by calmodulin (CaM). Here we use a combination of biochemical methods and NMR spectroscopy to probe the interaction between AQP0 and CaM. We show that CaM binds the AQP0 C-terminal domain in a calcium-dependent manner. We demonstrate that only two CaM molecules bind a single AQP0 tetramer in a noncanonical fashion, suggesting a form of cooperativity between AQP0 monomers. Based on these results, we derive a structural model of the AQP0/CaM complex, which suggests CaM may be inhibitory to channel permeability by capping the vestibules of two monomers within the AQP0 tetramer. Finally, phosphorylation within AQP0's CaM binding domain inhibits the AQP0/CaM interaction, suggesting a temporal regulatory mechanism for complex formation.
KW - PROTEIN
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U2 - 10.1016/j.str.2008.06.011
DO - 10.1016/j.str.2008.06.011
M3 - Article
C2 - 18786401
AN - SCOPUS:50849097568
SN - 0969-2126
VL - 16
SP - 1389
EP - 1398
JO - Structure
JF - Structure
IS - 9
ER -